Although the physical layout of a network will to some extent be determined by its size and the type of networking technology chosen, the cabling system is a critical element of any network. It is generally accepted that a significant number of network failures are caused primarily by cable-related problems. Getting the cabling system right, therefore, is essential for an effective data communications system. The standards define how to design, build, and manage a cabling system that is structured, meaning that the system consists of a number of discrete sub-systems or blocks, each of which has specific performance characteristics. The blocks are organised hierarchically within a unified communication system. A workgroup LAN block, for example, has lower-performance requirements than a network backbone block, which usually requires high-performance fibre-optic cable. The standards have evolved to support high-speed networking technologies such as Gigabit Ethernet, and advanced cable types such as Category 6 and Category 7 twisted pair cable. Structured cabling or premise wiring defines a generic telecommunication wiring system for commercial buildings, and comprises the cabling, connectors and accessories used to connect local area network and telephone system equipment within a building. It breaks cabling systems down into two main elements, horizontal wiring and vertical (or backbone) wiring. Structured cabling standards define the media, topology, termination and connection points, and administrative practice to be used.